Contrary to ordinary steel plates, a steel section has a complicated cross-sectional shape, and its shape after hot rolling and cooling shows peculiar bends.
A steel section is used mainly for construction and shipbuilding materials, and its straightness and good shape are important requirements for such uses, and in addition, with the advance of automation techniques (numerical control, etc.) of processing machines in recent years, the straightness and the precision of the shape of steel sections have been further required. Accordingly, straightening after hot rolling and cooling is required so as to give an extremely high degree of straightness to such finished steel products.
In a conventionally known straightening machine for steel sections, as shown in FIG. 1 and FIG. 2, straightening rollers 2, 2' are arranged zigzag or offset in the vertical direction and guide rollers A and B having vertical axes for controlling right and left movements of the material 1 at inlet and outlet sides of the group of straightening rollers 2, 2'.
In such a conventional roller straightening machine, surfaces which will suitably contact the cross-sectional shape of material are formed on upper and lower straightening rollers 2, 2', which are arranged so as to be displaced in the vertical direction as well as in the axial direction.
However, in such a conventional roller straightening machine as mentioned above, positive and negative bends may be sufficiently given in the vertical direction or the like, so that straightening effect in that direction may be obtained, but straightening effect in the horizontal direction perpendicular to the direction of advance of the material 1 is not sufficient in view of its mechanism. This is attributable to the fact that as shown in FIG. 4, for instance, in a steel section, such as an angle with unequal legs (hereinafter, simply called an "invert"), having a section with large rigidity in right and left directions and large bends in right and left directions (seen from the direction in FIG. 4), if the straightening rollers 2, 2' are displaced and adjusted in the axial direction so as to effect bending, the material 1 will be off from the pass-line of the group of straightening rollers by repulsive force due to rigidity of the material and will shift and pass in the axial direction of straightening rollers, as shown in the drawing, resulting in an insufficient, straightening force in the right and left directions.
To correct this defect, straightening of a steel section in a cross-sectional posture is effected as an example shown in FIG. 5(b), wherein the material 1 (FIG. 5(a ) ) is apt to undergo abnormal deformation due to buckling as shown in FIG. 5(c), furthermore threading of the material 1 through the group of straightening rollers in such a cross-sectional posture (in this case, FIG. 5(a) ) is difficult, so that the working property is considerably hindered.